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TPS3890: TPS389018 - MR pin voltage while Vdd is floating/not available

Sunset
Genius 13395 points
Part Number: TPS3890

Hello Team,

does the TPS389018 have problems if the MR pin get 3.3V while Vdd is not yet getting 3.3V?

In particular Vdd and MR voltages, come from two different power supplies.

MR gets for short time 3.3V at low impedance (without a pull up resistor), while Vdd is not yet there.

By measuring the MR current it looks that only 10uA flows at 3.5V, thus it looks ok.

Nevertheless the TPS389018 ESD structure is not clear and is not sure if 10uA will always be that and not higher.

Currently a redesign would be needed if a resistor or diode will be added in serie with MR to avoid the problem.

  • can you confirm that 3.3V on MR, without Vdd is not a problem?
  • If a resistor to limit the current is required, to which value must be that current be limited?

Thanks for the follow up,

SunSet

  • 0
    TI__Genius 9375 points

    Hi Sunset,

    /MR should be okay being initiated before Vdd. The RESET will then obviously not be impacted by MR until VDD reaches VDD(min), but there should be non-significant amounts of current sink in this case. This case has not to my knowledge been tested by our team however, so I would ask the customer to verify currents on each pin during operation. Since MR does not require a pullup resistor, it should not in this case as well.
    Let me know if you have additional thoughts.

    Thanks,
    Abhinav.